Weed

weedsvegetable pestsweedy speciesagricultural weedenvironmental weedfitchesherbaceous weedsinvasive plantland weedsnoxious weed
A weed is a plant considered undesirable in a particular situation, "a plant in the wrong place".wikipedia
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Beneficial weed

Many plants that people widely regard as weeds also are intentionally grown in gardens and other cultivated settings, in which case they are sometimes called beneficial weeds.
A beneficial weed is an invasive plant not generally considered domesticated (however, some plants, such as dandelions, in addition to growing wild, are commercially cultivated) that has some companion plant effect, is edible, contributes to soil health, adds ornamental value, or is otherwise beneficial.

Weed control

weedingweedweed management
Weed control is important in agriculture.
Weed control is the botanical component of pest control, which attempts to stop weeds, especially noxious or injurious weeds, from competing with desired flora and fauna, this includes domesticated plants and livestock, and in natural settings, it includes stopping non local species competing with native, local, species, especially so in reserves and heritage areas.

Garden

gardenspublic gardenflower beds
Examples commonly are plants unwanted in human-controlled settings, such as farm fields, gardens, lawns, and parks.
Natural elements present in a garden principally comprise flora (such as trees and weeds), fauna (such as arthropods and birds), soil, water, air and light.

Cultivator

rotary tillerrototillercultivating
Methods include hand cultivation with hoes, powered cultivation with cultivators, smothering with mulch, lethal wilting with high heat, burning, or chemical attack with herbicides.
Cultivators stir and pulverize the soil, either before planting (to aerate the soil and prepare a smooth, loose seedbed) or after the crop has begun growing (to kill weeds—controlled disturbance of the topsoil close to the crop plants kills the surrounding weeds by uprooting them, burying their leaves to disrupt their photosynthesis, or a combination of both).

Chrysolina

Chrysolina quadrigeminasome of its natural enemies
An example is Klamath weed, that threatened millions of hectares of prime grain and grazing land in North America after it was accidentally introduced, but was reduced to a rare roadside weed within several years after some of its natural enemies were imported during World War II. In locations where predation and mutually competitive relationships are absent, weeds have increased resources available for growth and reproduction.
All species of Chrysolina are phytophagous, feeding on specific food plants, and some of them have been used for biological control of weeds.

Hypericum perforatum

St John's wortSt. John's wortSt. John’s Wort
An example is Klamath weed, that threatened millions of hectares of prime grain and grazing land in North America after it was accidentally introduced, but was reduced to a rare roadside weed within several years after some of its natural enemies were imported during World War II. In locations where predation and mutually competitive relationships are absent, weeds have increased resources available for growth and reproduction.
Hypericum perforatum is native to temperate parts of Europe and Asia, but has spread to temperate regions worldwide as a cosmopolitan invasive weed.

Glechoma hederacea

ground ivyCreeping Charliealehoof
In contrast, perennial weeds often have underground stems that spread under the soil surface or, like ground ivy (Glechoma hederacea), have creeping stems that root and spread out over the ground.
It will form dense mats which can take over areas of lawn and woodland and thus is an considered invasive or aggressive weed in suitable climates where it is not native.

Chenopodium album

fat henlambsquarterswhite goosefoot
A number of weeds, such as the dandelion (Taraxacum) and lamb's quarter, are edible, and their leaves or roots may be used for food or herbal medicine.
Chenopodium album is a fast-growing weedy annual plant in the genus Chenopodium.

Invasive species

invasiveinvasive plant speciesinvasive plant
The term weed also is applied to any plant that grows or reproduces aggressively, or is invasive outside its native habitat.
Weeds reduce yield in agriculture, though they may provide essential nutrients.

Lawn

GrassturfgrassGrass pitch
Examples commonly are plants unwanted in human-controlled settings, such as farm fields, gardens, lawns, and parks.
An example of an organic herbicide is corn gluten meal, which releases an 'organic dipeptide' into the soil to inhibit root formation of germinating weed seeds.

Plant

plantsfloraplant kingdom
A weed is a plant considered undesirable in a particular situation, "a plant in the wrong place".
Weeds are unwanted plants growing in managed environments such as farms, urban areas, gardens, lawns, and parks.

Noxious weed

weednoxiousnoxious weeds
Some weed species have been classified as noxious weeds by government authorities because, if left unchecked, they often compete with native or crop plants or cause harm to livestock.
A noxious weed, harmful weed or injurious weed is a weed that has been designated by an agricultural authority as one that is injurious to agricultural or horticultural crops, natural habitats or ecosystems, or humans or livestock.

Allelopathy

allelopathicallelochemicalsallelochemical
The weediness of some species that are introduced into new environments may be caused by their production of allelopathic chemicals which indigenous plants are not yet adapted to, a scenario sometimes called the "novel weapons hypothesis".
It is sold to control broadleaf weeds in corn but also seems to be an effective control for crabgrass in lawns.

Rumex

dockdockssorrel
Sorrel – annual or perennial
Some are nuisance weeds (and are sometimes called dockweed or dock weed), but some are grown for their edible leaves.

Goldenrod

Solidagogoldenrodsgolden rod
Goldenrod – perennial
They are considered weeds by many in North America, but they are prized as garden plants in Europe, where British gardeners adopted goldenrod as a garden subject long before Americans did.

Toxicodendron radicans

poison ivypoison-ivyAmerican poison ivy
Poison ivy – perennial
T. radicans is commonly eaten by many animals, and the seeds are consumed by birds, but poison ivy is most often thought of as an unwelcome weed.

Cynodon dactylon

Bermuda grassBermudabermudagrass
Bermuda grass – perennial, spreading by runners, rhizomes and seeds.
It is also highly aggressive, crowding out most other grasses and invading other habitats, and has become a hard-to-eradicate weed in some areas (it can be controlled somewhat with Triclopyr, Mesotrione, Fluazifop-p-butyl, and Glyphosate).

List of beneficial weeds

beneficial weeds
List of beneficial weeds
This is a list of undomesticated or feral plants, generally considered weeds, yet having some positive effects or uses, often being ideal as companion plants in gardens.

Euphorbia virgata

leafy spurge
Leafy spurge – perennial, with underground stems
It has been identified as a serious weed on a number of national parks and on reserves of The Nature Conservancy in eleven northern states.

Crop weed

agricultural weed
Crop weeds
Crop weeds are weeds that grow amongst crops.

Vavilovian mimicry

mimicsecondary cropVavilovian
Vavilovian mimicry
Vavilovian mimicry (also crop mimicry or weed mimicry ) is a form of mimicry in plants where a weed comes to share one or more characteristics with a domesticated plant through generations of artificial selection.

Weed of cultivation

Weed of cultivation
A weed of cultivation is any plant that is well-adapted to environments in which land is cultivated for growing some other plant.

Pest (organism)

pestpestsagricultural pest
Pest (organism)
Many weeds are also seen as useful under certain conditions, for instance Patterson's curse is often valued as food for honeybees and as a wildflower, even though it can poison livestock.

Trifolium repens

white cloverladinoclover
White clover is considered by some to be a weed in lawns, but in many other situations is a desirable source of fodder, honey and soil nitrogen.
As a leguminous and hardy plant, it is considered to be a beneficial component of natural or organic pasture management and lawn care due to its ability to fix nitrogen and out-compete weeds.

Volunteer (botany)

volunteervolunteer plantvolunteer plants
Volunteer (botany)
Unlike weeds, which are unwanted plants, a volunteer may be encouraged by gardeners once it appears, being watered, fertilized, or otherwise cared for.